In this project the viscoelastic properties of molten salts at gigahertzian frequency has been investigated. Research projects were successfully carried out in two years. Major accomplishments are summarized as follows.(1)Ultrasonic velocity and absorption coefficient of molten alkali carbonates and nitrates have been measured. The compressibility and internal pressure have been derived from the ultrasonic velocity. Bulk viscosity, which can be attributed to the structural relaxation, has been derived from the absorption coefficient. There is not disperssion in the sonic velocity at the magahertzian frequencies. This fact indicates that the relaxation frequencies of molten alkali carbonates and nitrates are higher than the submagahertz.(2)Hypersonic velocity of ZnCl_2-NaCl and ZnCl_2-KCl binary melts has been measured in the temperature ranges covering about 150K above the liquidus temperatures of the melts over the composition ranges of 0 to 50mol% NaCl and KCl by means of the Brillou
… Morein scattering method. The Hypersonic velocity of ZnCl_2 decreases linearly with increasing temperature at the high and the low temperature regions, but at the intermediste temperatue region, shows a curvilinear temperature dependence, indicating dispersion of sound propagation at the gigahertzian frequencies. The dispersion behavior observed is well described in terms of the single relaxation theory. It was found that the relaxation frequency of the binary melts increases steeply with an addition of NaCl and KCl. This is considered to be due to the depolymerization of the network structure in the melts.(3)The complete profiles of Rayleigh-Brillouin spectra of ZnCl_2-NaCl binary melts were obtained for the first time by the use of the carefully purified sample. The remarkable change in the shape of the spectrum with temperature and composition variation has been observed and has been concluded to be due to a structural relaxation in the melts. The spectra have been analyzed by the viscoelastic theory on the assumption of a single relaxation. The sound velocities at limiting low and high frequencies and the relaxation times have been determined. Less